The present invention relates to the separation of components from aromatic hydrocarbon mixtures thereof by extractive distillation.
Extractive distillation is a process to separate close-boiling compounds from each other by introducing a selectively-acting third component, the extractive distillation solvent, with the result that the relative volatility of the mixture to be separated is increased and azeotropes, if present, are overcome. The extractive distillation solvent is to be selected such that it does not form an undesired azeotrope with any of the compounds in the mixture.
As an example, the separation of C7, C8-isomers (non-aromatic hydrocarbons) and toluene (aromatic hydrocarbons) is complicated due to low relative volatilitles or the existence of an azeotrope. Aniline or phenol have been proposed in the literature as extractive distillation solvents to produce C7, C8-isomers as distillate.
As an example, the separation of benzene (aromatic hydrocarbons) and cyclohexane (naphtenes) is complicated due to the existence of an azeotrope. Aniline has been proposed in the literature as extractive distillation solvents to produce cyclohexane as distillate.
As has been stated in U.S. Pat. No. 5,800,681 (Berg) extractive distillation is the method of separating close boiling compounds from each other by carrying out the distillation in a multiplate rectification column in the presence of an added liquid or liquid mixture, said liquid(s) having a boiling point higher than the compounds being separated. The extractive distillation solvent is introduced near the top of the column and flows downward until it reaches the stillpot or reboiler. Its presence on each plate of the rectification column alters the relative volatility of the close boiling compounds in a direction to make the separation on each plate greater and thus require either fewer plates to effect the same separation or make possible a greater degree of separation with the same number of plates. The extractive distillation solvent should boil higher than any of the close boiling liquids being separated and not form minimum azeotropes with them. Usually the extractive distillation solvent is introduced a few plates from the top of the column to ensure that none of the extractive distillation solvent is carried over with the lowest boiling component.
It is an object of this invention to suggest at least one further extractive distillation solvent for the separation of components from mixtures thereof.
According to the invention, a method of separation of aromatic hydrocarbons and non-aromatic hydrocarbons, includes the step of distilling a mixture of aromatic hydrocarbons and non-aromatic hydrocarbons containing at least aromatic hydrocarbons and non-aromatic hydrocarbons by way of an extractive distillation process in the presence of an extractive distillation solvent being an ester of a dibasic acid.
The aromatic hydrocarbons and non-aromatic hydrocarbons mixture may contain only aromatic hydrocarbons and non-aromatic hydrocarbons.
The non-aromatic hydrocarbons may be at least one of the compounds selected from a group consisting of C7-isomers and C8-isomers.
The aromatic hydrocarbons may be toluene.
The ester of a dibasic acid may be selected from a group consisting of dimethylmaleate and dimethylphtalate.
Also according to the invention, a method of separation of aromatic hydrocarbons and non-aromatic hydrocarbons includes the step of distilling a mixture of aromatic hydrocarbons excluding benzene and non-aromatic hydrocarbons containing at least aromatic hydrocarbons excluding benzene and non-aromatic hydrocarbons by way of an extractive distillation process in the presence of an extractive distillation solvent being N-methyl 2-pyrrolidone.
The aromatic hydrocarbons/non-aromatic hydrocarbons mixture may contain only aromatic hydrocarbons and non-aromatic hydrocarbons.
The non-aromatic hydrocarbons may be least one of the compounds selected from a group consisting of C7-isomers and C8-isomers.
The aromatic hydrocarbons may be toluene.
The non-aromatic hydrocarbons may be naphtenes and the extractive distillation solvent may be selected from the group consisting of a dione, an ester of a dibasic acid and a morpholine.
The aromatic hydrocarbons and naphtenes mixture may contain only aromatic hydrocarbons and naphtenes.
The aromatic hydrocarbons may be benzene.
The naphtenes may be cyclohexane.
The dione may be acetonyl acetone.
The ester of a dibasic acid may be selected from a group consisting of dimethylmaleate and dimethylphtalate.